1. Field of the Invention The present invention relates to a tracking system for a magnetic recording/reproducing apparatus of helical scanning type.
2. Description of the Prior Art
In a magnetic recording/reproducing apparatus used for recording and reproducing video signals such as a VTR, recording of very fine video signals and digital recording of NTSC signals have recently been under study. Since these signals require a drastically large amount of information to be recorded compared with the analog NTSC signals, high density recording is wished strongly. As a means to achieve high density recording, there are a method in which the wave length to be recorded on a magnetic tape is reduced and a method in which the track width of a recording track to be formed on a magnetic tape is narrowed However, when the recording track width is narrowed in order to improve the recording density, if a reproducing apparatus is different from a recording apparatus, the scanning locus of the rotating magnetic head becomes different due to mechanical errors and the like between the apparatuses, so that it becomes difficult for the rotating magnetic head to accurately scan over the recording track during reproduction, making it impossible to achieve reproduction of video signals with good S/N.
In order to solve the above problem, a conventional system in which a rotating magnetic head and a piezo-electric element are constructed as an integral component and the piezo-electric element is driven during reproduction according to a tracking error signal so as to cause the rotating magnetic head to be displaced in the track width direction thereby causing the rotating magnetic head to accurately scan over recording tracks.
In a conventional system such as above, there are the following problems. (1) A brush and a slip ring for supplying driving power to a rotating piezo-electric element must be constructed on a rotary drum. Precious metals must be used for the contacting part of the brush and the slip ring in order to secure reliability, which inevitably increases cost of the apparatus. Also because the brush and the slip ring are to be provided on the rotary drum the height of the rotary drum will be increased and it becomes difficult to realize a thin magnetic recording/ reproducing apparatus. (2) Generally, to achieve highly accurate tracking, the rotating head must be controlled accurately in the order to several microns, but it is difficult to realize highly accurate tracking because of the drifting distortion inherent to the piezo-electric element. (3) It is very difficult to cause the head to be displaced in a direction parallel to the direction of the track width. For this reason, the space between the head and the tape is increased, so that the reproduced output of a short wave signal in particular is lowered.
In order to solve the above problems of the conventional system, a system is proposed in which the longitudinal position of the magnetic tape is made to be variable without causing the rotating head to be displaced. (Japanese Laid-Open Patent Applications No. 60-175240 (1985), and No. 60-185244 (1985)) In this system, only a tape running mechanism arranged with a means which makes the tape position variable between a rotating magnetic head and a capstan, is used. Though this system employs an effective means to make the longitudinal position of the magnetic tape to be variable thereby causing the rotary magnetic head to scan accurately over the recording track, there still remains a number of problems before realizing such system as a magnetic recording/reproducing apparatus.